Yol. 52.] ANNIVERSARY ADDRESS OE THE PRESIDENT. ci 



rudimentary thumb. The hinder margin of the carapace is over- 

 lapped at the sides by the first segment of the abdomen. 



It seems probable that Udorella Agassizi, from the Lithographic 

 Stone of Solenhofen, belongs here : the feet are monodactylous, but 

 the outer antennae each have two flagella, and the thoracic feet 

 carry endopodites externally, which may be gills as in Mysis. 

 Pseudocrangon tenuicaudus, from the Chalk of Westphalia, should, 

 I think, be placed here. 



The position of Paloeocrangon eskdalensis, from the Lower Carboni- 

 ferous of Scotland, is very doubtful. 



Mesocrangon atra is from the Gault of Folkestone, and Pseudo- 

 crangon from the Chalk of the Lebanon. 



The Pen^idea, typified by the genus Penceus, are a group 

 abundantly represented in the Secondary rocks. The oldest form 

 is probably the Penceus liassicus, Oppel, from the Lower Lias, 

 Schambelen, Switzerland, and next comes P. Sharjpii, H. Woodw., 

 from the Upper Lias of Northampton. There are, moreover, five 

 well-preserved species, figured and described by Oppel from the 

 Lithographic Stone of Solenhofen. Acanthochirus 3 species, Bylgia 

 3 species, Drobna 2 species, and Dusa ? 3 species, are also considered 

 to belong to the Penseidse. Penceus septemspinatus, Dames, and 

 P. libanensis, Brocchi, are from the Cretaceous of the Lebanon. 



Penceus and 20 other genera allied to it are living at the present 

 day very widely distributed geographically. The New South Wales 

 species, P. esculentus, attains a length of 9 inches, and is largely used 

 for food. The genus is of especial interest, not only as occurring 

 fossil, or as being edible, but from the fact that, so far as we at 

 present know, it is the only Macrurous Decapod in which the 

 young passes from the egg as a simple Nauplius-l'dXYa., similar to 

 that of a young Copepod, Cirripede, or Phyllopod-larva just hatched 

 from the egg, and advances through a series of moults to a Mysis- 

 formed zoea before attaining the adult stage. 



Astacidea. — Of the section Astacidea, the Eryontidae occupy the 

 first family, but they are peculiar and vary considerably from the 

 ordinary type. 



Eryontidae. — The genus Eryon was first made known by Des- 

 marest in 1822, and was applied by him to a group of Macrurous 

 Crustacea with a broad and flat carapace, strongly notched or indented 

 around the anterior border, but with straight sides ; the antennules 

 are small, and bear multiarticulate flagella : there is a narrow scale 

 near the base of each outer antenna, the flagellum being of moderate 

 vol. hi. h 



